I had an MX Performance and got a faulty button and took it back, it felt odd and looked cheap compared to the older Revolution. Which at the time, I still had 2 of. When one Revolution died (one is for my desktop, the bluetooth version for the laptop), I mixed the two together to make one good one, and bought a g700. Other than working on glass, I got the impression that the Performance was not much of an upgrade to the Revolution, but a way to bring in the new technology, and in order to do so, they cut costs elsewhere. The Revolution was a great mouse, and they are actually pretty well cherished by owners and command a good price still because of it.
As for the g700, I dislike the looks of it (and the newer S) and it took a bit to adjust to the feel, but as Typo said, it actually is a better mouse. I thought it felt and looked cheap, but that's only the outside, after taking one apart, it couldn't be further from the truth. Inside is a VERY well made mouse. On top of what Typo said, you can use it wired or wireless, and even uses a common nihm battery that is easily replaced if you are in a jam. Like i said, I don't care for the looks, or need the extra buttons, but really, it's a fantastic mouse once you get past those two things. Arguably the best wireless mouse on the market, and in my opinion, one of the best mice made in general.
I do recommend upgrading the battery though, I put a 2700mah in mine and it can handle 12+ of hard work, at mid to high resolution.